1. Field of the Invention
This invention relates to a process for the preparation of finely divided solid polyisocyanates containing urea groups by the reaction of organopolyisocyanates which are free from urea groups with water in the presence of a stabilizing compound containing at least one hydrophilic and at least one isocyanate reactive group and optionally in the presence of conventional emulsifiers and/or catalysts and/or bases.
2. Description of the Prior Art
Processes for the preparation of solid polyisocyanates containing urea groups by the reaction of organic polyisocyanates which are free from urea groups with an excess of water as reactive medium are already known (inter alia U.S. Pat. No. 3,906,019). Since in these processes the reaction products immediately cake together and are therefore difficult to work up and process, attempts have been made to prepare these reaction products in a finely divided form and in quantitative yields. According to the teaching of DOS No. 3,438,527, this object may be achieved by carrying out the reaction in the presence of a high molecular weight protective colloid such as a polyacrylate, cellulose, polyvinyl alcohol, etc. Although these high molecular weight protective colloids are highly effective, their solubility in water may cause long production runs. Moreover, the protective colloids are liable to be deposited as a film on the surface of the polyisocyanates containing urea groups, thereby impairing the reactivity of these polyisocyanates, especially if they are kept in storage for some time.
It is therefore an object of the present invention to provide a process for the preparation of polyisocyanates containing urea groups wherein the reaction products are not only obtained quantitatively in a very finely divided form but are also not impaired in their reactivity.